Access point power control

ABSTRACT

There is described a method of controlling a basestation in a cellular wireless communications network, the method comprising, within the basestation, autonomously and dynamically adapting a maximum value for a total transmit power of the basestation, such that interference between the basestation and other access points in the vicinity is minimized.

This divisional application claims priority to U.S. patent applicationSer. No. 13/214,084, filed on Aug. 19, 2011, and entitled “ACCESS POINTPOWER CONTROL”, which is a continuation of U.S. patent application Ser.No. 11/801,337, filed on May 8, 2007, now U.S. Pat. No. 8,032,142,issued on Oct. 4, 2011, and entitled “ACCESS POINT POWER CONTROL”, whichis hereby incorporated by reference and for all purposes.

This invention relates to an access point, acting as a basestation in acellular wireless communications network, and in particular to such anaccess point, in which maximum transmit power levels of the access pointare controlled in such a way as to avoid interference while ensuringacceptable coverage.

In conventional cellular networks, basestations are installed by thenetwork operators, in order to provide coverage for the areas where thenetwork operators expect there to be a demand for their services. Thenetwork planners are able to choose the locations of the basestations,and are able to set the maximum transmit powers, of the basestationitself and of the mobile devices that establish connections with thebasestation, in order to ensure a certain coverage and Quality ofService (QoS). To achieve these aims, the process requires detailed sitesurveys and geographical planning. When a maximum transmit power hasbeen set, this effectively sets the size of the cell served by thebasestation, because it determines the range over which thetransmissions from the basestation can successfully be received. Themaximum transmit power is rarely changed after it has initially beenset, but can be altered from the network if necessary, for examplebecause of changes to the radio network.

When a maximum transmit power has been set for the basestation, andcalls are in progress, power control is also applied to thetransmissions within these calls. Firstly, an initial transmit power isset, for example based on the power of a received access request, andthereafter power control is applied to the transmissions, based onsignal strength measurements made by the mobile device involved in thecall and reported back to the basestation. Such power control canoperate very quickly. For example, the power level used by a basestationfor its transmissions can be adapted at a frequency in the kilohertzregion. That is, the power level can in theory change many times persecond if the signal strength measurements indicate this.

In the case of access points (also known as femtocell basestations),these are intended to be available for purchase by consumers themselvesfor location within a home or office, and are intended to providecellular coverage over relatively small geographical areas, for exampleonly within the building in which they are located. For such devices,costly site surveys and detailed radio network planning are notpossible. It is therefore proposed that such devices should be able toconfigure themselves, based on the local radio environment.

U.S. Pat. No. 6,314,294 relates to a basestation, in which RF transmitpower levels are self calibrated, using data collected by the wirelesssystem.

According to a first aspect of the present invention, there is providedmethod of controlling a basestation in a cellular wirelesscommunications network, the method comprising:

-   -   within the basestation, autonomously and dynamically adapting a        maximum value for a total transmit power of the basestation.

According to a second aspect of the present invention, there is provideda basestation adapted to perform the method according to the firstaspect of the invention.

This has the effect that the basestation can configure itself, based onthe local radio environment, with reduced network involvement.

For a better understanding of the present invention, and to show how itmay be put into effect, reference will now be made, by way of example,to the accompanying drawings, in which:

FIG. 1 is a block schematic diagram of a part of a cellular wirelesscommunications network.

FIG. 2 is a flowchart of a carrier-selection algorithm.

FIG. 3 is a flowchart of a scrambling code selection algorithm.

FIG. 4 is a flowchart of an algorithm for selecting the initial downlinkmaximum transmit power.

FIG. 5 is a flowchart of an algorithm for selecting the initial uplinkmaximum transmit power.

FIG. 6 is a flowchart of an algorithm for adapting the uplink anddownlink maximum transmit powers.

FIG. 7 is a flowchart of an algorithm for adapting the uplink anddownlink maximum transmit powers in the event that macrolayerinterference is detected.

FIG. 8 is a flowchart of an algorithm for adapting the uplink anddownlink maximum transmit powers in the event that no interference isdetected in the macrolayer or the femtocell basestation layer.

FIG. 1 illustrates a part of a cellular wireless communications networkin accordance with an aspect of the present invention. Specifically,FIG. 1 shows a core network (CN) 10 and a radio network (RN) 12 of acellular wireless communications network. These are generallyconventional, and are illustrated and described herein only to thelimited extent necessary for an understanding of the present invention.

Thus, the core network 10 has connections into the Public SwitchedTelephone Network (PSTN) (not shown) and into a packet data network, forexample the internet 14. The radio network 12 may include, for example,a GSM radio network and/or a UMTS radio network, which are thengenerally conventional. As shown in FIG. 1, the radio network 12 has abasestation (BS) 16 connected thereto. As will be recognized by theperson skilled in the art, a typical radio network 12 will have manysuch basestations connected thereto. These basestations provide coverageover respective geographic areas, or cells, such that a service isavailable to subscribers. Often, there is a group of basestations thattogether provide coverage to the whole of the intended service area,while other basestations provide additional coverage to smaller areaswithin that intended service area, in particular to smaller areas wherethere is expected to be more demand for the service. The cells served bythe basestations of the first group are then referred to as macrocells,while the smaller areas served by the additional basestations arereferred to as microcells.

FIG. 1 also shows an additional basestation 18 that can be used toprovide coverage over a very small area, for example within a singlehome or office building. This is referred to as a femtocell basestation(FBS). The femtocell basestation 18 is connected into the mobile networkoperator's core network 10 over the internet 14, by means of thecustomer's existing broadband internet connection 20. Thus, a user of aconventional mobile phone 22 can establish a connection through thefemtocell basestation 18 with another device, in the same way that anyother mobile phone can establish a connection through one of the otherbasestations of the mobile network operator's network, such as thebasestation 16.

The core network 10 includes a management system (MS) 24 that providesinformation to the FBS 18, as described in more detail below.

As mentioned above, the macrocell basestations provide coverage to thewhole of the intended service area including the location of thefemtocell basestation 18 and the location of the mobile phone 22 whileit is in the coverage area of the femtocell basestation 18. However, thenetwork is configured such that, when a mobile device that is registeredwith the femtocell basestation 18 is within the coverage area of thefemtocell basestation 18, then it will preferentially establish aconnection with the femtocell basestation 18 rather than with themacrolayer basestation 16.

When the femtocell basestation 18 is first powered on, it selects acarrier frequency and a scrambling code, from lists provided to it froma management system that generally controls the operation of thefemtocell basestations in the network. The carrier frequencies and thescrambling codes on the list are shared with other basestations in thenetwork, including nodeBs of the macrolayer and other femtocellbasestations, and so the carrier frequency and scrambling code arechosen such that they result in the lowest interference to neighbournodeBs of the macrolayer and neighbour femtocell basestations.

Thereafter, the basestation can autonomously and dynamically select itscarrier frequency from the permitted set of carrier frequencies, and canautonomously and dynamically select its scrambling code from a permittedset of codes, in order to produce the lowest interference (see FIGS. 2and 3).

Also, the femtocell basestation 18 selects an initial value for themaximum total downlink power, and for total mobile transmit power levels(see FIGS. 4 and 5). This initial value can be preset in the femtocellbasestation 18, based for example on an assumption about the type oflocation in which the device will be used. For example, it may beassumed that the device will generally be used in homes or smalloffices, up to a particular size (for example 90 to 250 m²), and furtherassumptions can then be made about the signal attenuation that willresult, and this can be used to determine what value should be set forthe maximum total downlink power, in order to ensure a reasonablecoverage throughout that area, while avoiding interference withneighbour nodeBs of the macrolayer and neighbour femtocell basestations.

Again, the femtocell basestation 18 can autonomously and dynamicallyadapt both its total transmit power (including the transmit power ofcontrol channels as well as traffic channels) and the total transmitpower of the mobiles attached to the basestation.

It is well known that power control should be applied in a cellularcommunications system, so that the transmission powers in the uplink(UL) and downlink (DL) directions can be adjusted quickly, in order totake account of rapid changes that affect each communication path fromthe basestation to the relevant mobile device. In the UMTS system, thegroup of functions used to achieve this are: open-loop power control,inner-loop (or fast) PC and outer-loop power control in both UL and DLdirections. Slow power control is also applied to the DL commonchannels. Open-loop power control is responsible for setting the initialUL and DL transmission powers when a UE is accessing the network. Thereare two types of inner-loop power control algorithms both of whichadjust the transmission dynamically on a 1500 Hz basis. The outer-looppower control estimates the received quality and adjusts the target SIR(signal-interference ratio) for the fast closed-loop power control sothat the required quality is provided.

However, in accordance with aspects of the present invention, the totaltransmit power of the basestation (including the transmit power ofcontrol channels as well as traffic channels) and the total transmitpower of the mobiles attached to the basestation are also adaptivelycontrolled autonomously by the basestation itself.

This control can for example take place on the basis of measurementsmade by the basestation itself. That is, the basestation is able todetect signals transmitted by other basestations, including macrolayerbasestations and other femtocell basestations. The basestation canidentify whether a detected interferer is a macrolayer basestation or afemtocell basestation based on identity information conveyed in thereceived broadcast channel of said interferer and RF signal measurementstherefrom. Preferably, the basestation suspends its own transmissionstemporarily in order to make these measurements, both when it isinitially powered on, and then intermittently during operation.

Thus, at power up the RSCP (Received Signal Code Power) values can bedetermined for the CPICHs (Common Pilot Channels) of all surroundingfemtocell basestations and macrolayer nodeBs for all available carriers.The carrier exhibiting the lowest interference is selected, where thelowest interference is defined as follows.

FIG. 2 is a flowchart showing the preferred algorithm by which thefemtocell basestation may select the initial carrier.

In the first step 50, the interference is calculated for each of theallowed carriers on the macrolayer (ML) and each of the allowed carrierson the femtocell basestation layer (FBL). The macrolayer interferencefor each carrier is calculated by determining the macrolayer CPICH_RSCPsin milliwatts for each detected scrambling code in each carrier. Theseindividual macrolayer CPICH_RSCPS are added together to calculate thetotal macrolayer interference power per carrier. This value is thenconverted back to dBm.

A similar method is used for determining the femtocell basestation layerinterference for each carrier. The femtocell basestation layerCPICH_RSCPs are determined in milliwatts for each detected scramblingcode in each carrier. These individual femtocell basestation CPICH_RSCPsare added together to calculate the total femtocell basestationinterference power per carrier. This value is then converted back todBm.

In the next step 52, it is determined whether there is more than oneallowed carrier.

If there is only one allowed carrier, the process moves to step 54, thatof determining whether the macrolayer interference for that carrier isbelow a maximum macrolayer interference threshold. If it is, the carrieris selected by the femtocell basestation. If the interference is abovethe threshold, an error is generated.

If there is more than one allowed carrier, the process moves to step 56,that of determining whether any of the allowed carriers on themacrolayer are currently unused. Hereinafter, a carrier is consideredunused on the macrolayer if there are no detected nodeB CPICH signalsand received signal strength indicator (RSSI) on the carrier is below aminimum macrolayer interference threshold.

If there are allowed carriers unused on the macrolayer, the process thendetermines in step 58 whether or not there are any allowed carriers onthe femtocell basestation layer. Hereinafter, a carrier is consideredunused on the femtocell basestation layer if there are no detectedfemtocell basestation CPICH signals and the RSSI on the carrier is belowa minimum femtocell basestation layer interference threshold. If thereare unused allowed carriers on the femtocell basestation layer, thefemtocell basestation layer carrier with the lowest RSSI is chosen. Ifthere are no unused allowed carriers on the femtocell basestation layer,the femtocell basestation layer carrier with the lowest interference (ascalculated in step 50) is chosen.

In step 56, if it is determined that there are no unused carriers on themacrolayer, the process moves to step 60, where the carrier with theleast macrolayer interference (as calculated in step 50) is chosen. Instep 62, the macrolayer interference of this carrier is compared with amaximum macrolayer interference threshold. If the interference is belowthe threshold, that carrier is chosen. If the interference is above thethreshold, an error is generated.

Once the carrier has been selected then, from the list of availablescrambling codes, a code is selected. For example, the CPICH_RSCPs ofall the available codes may be ranked, and the code with the lowestCPICH_RSCP value selected.

FIG. 3 is a flowchart showing the preferred algorithm by which thescrambling code may be selected. This algorithm will typically beapplied after the carrier selection algorithm described above withreference to FIG. 2.

In step 70, the interference for each allowed scrambling code for theselected carrier is calculated. This step is performed by grouping andsumming, by scrambling code, the detected femtocell basestation CPICHRSCPs for each basestation using the selected carrier.

In step 72, the process determines whether or not there are anyscrambling codes that are not being used by the detected femtocellbasestations. If there are any unused codes, one of these is chosen asthe scrambling code. The selection of scrambling code from the list ofunused codes is randomized to minimize the probability of two collocatedaccess points selecting the same code.

If there are no unused codes the process moves to step 74, where thecode with the least interference (as calculated in step 70) is selected.If the interference on this code is less than a maximum threshold, thatcode is chosen. If the interference is above the maximum threshold, anerror is generated.

Further, the initial selection of carrier and scrambling code could bechanged based on measurements from the UE. The UE may reportmeasurements from an adjacent carrier that may indicate that the initialcarrier or scrambling code were not optimal due to local shadowing ofthe femtocell basestation.

Following the carrier and code selection algorithms, the radiomeasurement data is reported back to the central management system,where it is checked against specified thresholds. If it is determinedthat the interference levels for the selected code/carriers exceed apredefined threshold set by the management system, and hence that thebasestation is not in a location where it can perform acceptably, anerror message is supplied to the user, suggesting a repositioning of theunit to a more optimal position within the home.

The initial maximum power values can then be set. If the macrolayerinterference dominates, then the initial maximum Down Link transmitpower is set based on the strongest macrolayer CPICH RSCP level andincluding a nominal in-door path loss of typically 60dB. Alternatively,if a carrier is selected which has little or no macrolayer interference,the maximum DL transmit power is set at the same level as the neighbourfemtocell basestation exhibiting the strongest CPICH RSCP level (i.e.the largest femtocell basestation interferer). This is done to maintainthe same QoS for collocated femtocell basestations. If there is neithermacrolayer or femtocell basestation interference, then the initialmaximum DL transmit power is set according to the expected UEsensitivity (for a mid range data service) including a nominal indoorpath loss of 60dB. This is different to existing Radio Access Network(RAN) design practice, in which the maximum DL Transmit power is set bya RF planner to ensure the expected coverage.

The maximum Up Link femtocell basestation UE transmit power is firstlycalculated by determining the smallest path loss to the neighbouringmacrolayer nodeB, typically the closest. By summing the minimummacrolayer nodeB sensitivity with the smallest path loss, the maximum ULTx power can be calculated. This method keeps the noise rise caused bythe femtocell basestation UE below the noise caused by the macrolayercell traffic. Likewise if no macrolayer interference is detected thenthe femtocell basestation sets its maximum DL transmit power at the samelevel as the neighbour femtocell basestation exhibiting the strongestCPICH RSCP level. If there is neither macrolayer or femtocellbasestation interference then the initial UL transmit power is setaccording to the femtocell basestation sensitivity (for a mid range dataservice) and a nominal path loss of 60 dB. Again, this is quitedifferent to existing Radio Access Network (RAN) design, in which themaximum UL Transmit power is set by a RF planner to ensure the expectedcoverage and UE battery life.

FIG. 4 is a flowchart showing the preferred algorithm by which thefemtocell basestation may select the initial DL maximum transmit power.

In step 100, the interference is calculated for the selected carrier onthe femtocell basestation layer and the macrolayer. This step willalready have been performed during the carrier-selection algorithm (step50 in FIG. 2).

In step 102, it is determined whether the selected carrier is unused onthe macrolayer and the femtocell basestation layer. Again, this stepwill already have been performed during the carrier-selection algorithm(steps 56 and 58 in FIG. 2).

If the carrier is unused on the macrolayer and the femtocell basestationlayer, the initial DL maximum transmit power is set at UE_(Prx, min),the average minimum signal power required by a femtocell basestation UEto support a particular data or speech service, plus the minimum indoorloss, a parameter corresponding to the allowed indoor path loss thatwill provide the required coverage (step 104). The minimum indoor lossis supplied by a central management system.

If the selected carrier is not unused by the macrolayer or the femtocellbasestation layer, the process moves to step 106 where the macrolayerinterference is compared with the femtocell basestation interference forthe selected carrier. If the macrolayer interference is greater, in step108 the initial DL maximum transmit power is set at the minimum indoorloss (as described above), plus the RSCP value of the nodeB with thelargest detected RSCP, minus 10×log₁₀(percentage of the total femtocellbasestation power allocated to CPICH).

The percentage of the total downlink transmission power allocated to theCPICH is a parameter supplied by the central management system.

If, in step 106, it is determined that the femtocell basestationinterference is greater than the macrolayer interference, the initial DLmaximum transmit power is set in step 110 at the CPICH power of theneighbour femtocell basestation with the largest detected RSCP value,minus 10×log₁₀(percentage of the total femtocell basestation powerallocated to CPICH).

As before, the percentage of the total downlink transmission powerallocated to the CPICH is a parameter supplied by the management system.

Once the initial DL maximum transmit power has been set in one of steps104, 108 or 110, the process checks in step 112 whether the initial DLmaximum transmit power is greater than or less than the maximumpermitted femtocell basestation DL power (a parameter set by themanagement system). If it is less than the maximum permitted power, theinitial DL maximum transmit power remains at its original value.However, if the initial DL maximum transmit power is greater than themaximum permitted power, the initial DL maximum transmit power is resetat the maximum permitted power, and a warning sent to the managementsystem. For example, a flag may be set to indicate that the initial DLmaximum transmit power is less than that required to run a particularspeech or data service, or that the DL power is currently at its maximumpermitted level.

FIG. 5 is a flowchart showing the preferred algorithm by which thefemtocell basestation may select the initial UL maximum transmit power.

Steps 150 and 152 are calculating the interference for the selectedcarrier on the femtocell basestation later and the macrolayer, andchecking whether the selected carrier is in use on the femtocellbasestation layer or the macrolayer, respectively. Both of these stepswill have been carried out earlier as part of the carrier selectionalgorithm, and are described in more detail with reference to FIG. 2.

If the carrier is not in use on the macrolayer or the femtocellbasestation layer, the initial UL maximum transmit power is set in step154 at FB_(Prx, min), the average minimum signal power required by afemtocell basestation to support a particular data or speech service,plus the minimum indoor loss, the allowed indoor path loss that willprovide the required coverage.

If the carrier is in use on the femtocell basestation layer or themacrolayer, the process moves to step 156, where the macrolayerinterference is compared with the femtocell basestation layerinterference for the selected carrier. If the femtocell basestationinterference is greater, the initial UL maximum transmit power is set instep 158 at the maximum UE transmit power of the femtocell basestationwith the least path loss. This value is determined by first calculatingthe path losses from the femtocell basestation to the detected femtocellbasestations using the following equation:

L _(FB-FB) =CPICH _(—) Tx_Power_(FB) −CPICH _(—) RSCP _(FB)

where CPICH_Tx_Power_(FB) is the CPICH transmitted power read from thebroadcast channel of detected femtocell basestations. The maximum UEtransmit power read from the broadcast channel of the neighbourfemtocell basestation that has the least path loss to the femtocellbasestation is then selected.

If the macrolayer interference is greater than the femtocell basestationinterference for the selected carrier, the nodeB to femtocellbasestation path losses are then calculated in step 160. The path lossesare calculated using the following equation:

L _(NodeB FB) =CPICH _(—) Tx_Power_(NodeB) −CPICH _(—) RSCP _(NodeB)

where CPICH_Tx_Power_(NodeB) is the CPICH transmitted power read fromthe broadcast channel of detected nodeBs.

The initial UL maximum transmit power is set in step 164 atML_(Prx, min), the average minimum signal power required by a nodeB tosupport a particular data or speech service, plus the RSCP value thatcorresponds to the least nodeB to femtocell basestation path loss.

Once the initial UL maximum transmit power has been set in one of steps154, 158 or 164, the process moves to step 166, where the initial ULmaximum transmit power is compared with the maximum permitted femtocellbasestation UL power. If the UL maximum transmit power is less than themaximum permitted power, the initial UL maximum transmit power ismaintained at its original level. If the UL maximum transmit power isgreater than the maximum permitted power, the initial UL maximumtransmit power is reset at the maximum permitted power as defined by themanagement system. Also, a warning is sent to the management system,that the UL power may be insufficient for certain data or speechservices, or that the UL power is currently at its maximum permittedlevel.

During operation, the maximum DL and UL transmit powers are adaptedthrough the regular CPICH RSCP and CPICH Ec/lo measurements reported bythe femtocell basestation UEs during idle mode or RRC connected mode(CELL_DCH state). The adaptation algorithm assumes that the femtocellbasestation UEs remain for the majority of the time within the expectedcoverage area (i.e. the house or office). The adaptation algorithmslowly increases or decreases the allowed UL and DL maximum transmitpower level to ensure that the CPICH Ec/lo (or QoS) remains at asuitable level for both speech and data services. In the case that thefemtocell basestation detects that there is local macrolayerinterference then over a period of time it builds two sets of histogramsfrom the femtocell basestation UE measurements of the active andneighbour cells. The first histogram is the path loss between thefemtocell basestation UE and the neighbour macrolayer nodeB and thesecond set of histograms is the path loss between the femtocellbasestation UE and the femtocell basestation and also the femtocellbasestation UE CPICH Ec/lo measurements. The adaptation algorithmattempts to keep typically 90% of all femtocell basestation UE CPICHEc/lo measurements above a particular level (e.g. −10 to −15 dB) butwill only allow 1% of femtocell basestation UE to femtocell basestationpath loss measurements (i.e. largest path loss) to exceed the path lossbetween the femtocell basestation UE and macrolayer nodeB (i.e. smallestpath loss). Furthermore the adaptation algorithm will allow a maximumpath femtocell basestation to femtocell basestation UE path loss oftypically <90 dB for 95% of the time. By assuming that the UL and DLpath loss is reciprocal, the same adaptation algorithms are used to setthe maximum DL and UL transmit power levels.

The femtocell basestation may also gather UE measurements by ‘sniffing’periodically (for example every 100 seconds) by stealing a down linkframe.

FIG. 6 is a flowchart showing the preferred algorithm by which thefemtocell basestation may dynamically adapt the UL and DL maximumtransmit powers.

As described above, the femtocell basestation regularly takes UEmeasurements of the active and neighbour cells, and these are used asthe input for adapting the maximum transmit powers. By monitoring the UEmeasurements, in step 200, the process first determines whether therehas been a significant change on either the macrolayer or the femtocellbasestation layer's interference levels for the carrier and scramblingcode already selected. A significant change in this context means anychange that will require a new carrier and/or scrambling code to bereselected. Therefore, if a significant change is found, the processwill rerun the carrier-selection algorithm, thescrambling-code-selection algorithm and the initial power setupalgorithm described with reference to FIGS. 2, 3 and 4, respectively, instep 202.

Once these “power up” algorithms have been performed, the process movesto step 203, that of re-gathering samples of UE measurements so thatstep 200 can be performed again for the new carrier and/or scramblingcode.

If there is no significant change in the macrolayer or the femtocellbasestation layer, the process determines in step 204 whether or not thecarrier is used on the macrolayer. If the carrier is used on themacrolayer (i.e. interference is detected on the macrolayer), themacrolayer interference algorithm is used to adapt the power (see FIG.7).

If the carrier is not used on the macrolayer, the process determines instep 206 whether the carrier is used on the femtocell basestation layer.If the carrier is not used on the femtocell basestation layer (i.e.there is no interference on the femtocell basestation layer) the “nointerference” algorithm is used to adapt the power (see FIG. 8).

If the carrier is used on the femtocell basestation layer, the UL and DLmaximum transmit powers are set as follows.

The UL maximum transmit power is set at the maximum UE transmit power ofthe femtocell basestation with the least path loss. This value isdetermined by first calculating the path losses from the femtocellbasestation to the surrounding detected femtocell basestations. Themaximum UE transmit power read from the broadcast channel of thesurrounding femtocell basestation that has the least path loss to thefemtocell basestation is then selected.

The path losses are determined, as before, by the following equation:

L _(FB-FB) =CPICH _(—) Tx_Power_(FB) −CPICH _(—) RSCP _(FB).

The DL maximum transmit power is set at the CPICH Tx power of thefemtocell basestation with the largest detected RSCP value, minus10×log₁₀(percentage of the total femtocell basestation power allocatedto CPICH).

That is, if only interference from a neighbouring femtocell basestationis detected, the basestation uses the power of that neighbouringbasestation to set its own UL and DL maximum transmit powers.

FIG. 7 is a flowchart of the preferred algorithm that may be used toadapt the UL and DL maximum transmit powers in the event that macrolayerinterference is detected.

As described above, histograms are produced from the UE measurements.Specifically, these are the femtocell basestation UE to neighbouringnodeB path losses, the femtocell basestation to femtocell basestation UEpath losses, and the femtocell basestation UE CPICH Ec/lo measurements.From these histograms, the following quantities can be calculated:

Avg_(—) Ec/lo=the average of the top 10% femtocell basestation UE CPICHEc/lo values;

Avg_ML_Pathloss=the average of the bottom 1% nodeB to femtocellbasestation UE path losses;

Avg_FBL_Pathloss=the average of the top 10% FB to FB UE path losses;

Pathloss_adjustment=the absolute value of [½×(Avg_(—)FBL_Pathloss−Avg_(—) ML_Pathloss)]

Further, a new parameter, Indoor loss, is set to the value of minimumindoor loss, initially provided by the central management system.However, minimum indoor loss is adapted as the process of DL and ULmaximum power adaptation is repeated, as will be described in moredetail below.

In step 250, Avg_Ec/lo is compared with the desired femtocellbasestation UE CPICH Ec/lo. If Avg_Ec/lo is larger, then the processmoves to step 252, which compares Avg_ML_Pathloss with Avg_FBL_Pathloss.If Avg_ML_Pathloss is greater, the UL and DL maximum transmit powers arekept at the same level (step 254).

If Avg_ML_Pathloss is smaller than Avg_FBL_Pathloss, then the UL and DLmaximum transmit powers are set as follows (step 256). Maximum DL poweris set at the RSCP level of the largest detected nodeB RSCP value, minus10×log₁₀(percentage of the total femtocell basestation power allocatedto CPICH), plus the indoor loss, minus Pathloss_adjustment. Maximum ULpower is set at ML_(Prx, min), the minimum signal power required by thebasestation to support a particular data or speech service, plus theAvg_ML_Pathloss. Further, minimum indoor loss is re-set at the value ofIndoor loss minus Pathloss_Adjustment.

If it is determined, in step 250, that Avg_Ec/lo is less than thedesired femtocell basestation UE CPICH Ec/lo, the process moves to step258, where Avg_ML_Pathloss is again compared with Avg_FBL_Pathloss.

If Avg_ML_Pathloss is smaller, the maximum DL power is set in step 260at the RSCP value of the nodeB with the largest detected RSCP value,minus 10×log₁₀(percentage of the total femtocell basestation powerallocated to CPICH), plus the Avg_ML_Pathloss. The maximum UL power isset at ML_(Prx, min), the minimum signal power required by thebasestation to support a particular data or speech service, plus theAvg_ML_Pathloss.

If Avg_ML_Pathloss is greater than Avg_FBL_Pathloss, the maximum DLpower is set in step 262 at the RSCP value of the nodeB with the largestRSCP value, minus 10×log₁₀(percentage of the total femtocell basestationpower allocated to CPICH), plus the indoor loss and Pathloss_adjustment.The maximum UL power is set at ML_(Prx, min), the minimum signal powerrequired by a femtocell basestation to support a particular data orspeech service, plus the Avg_ML_Pathloss. Further, minimum indoor lossis re-set at the value of Indoor loss plus Path loss_Adjustment.

Once the maximum DL and UL powers have been set in one of steps 256, 260or 262, the process moves in parallel to steps 263 and 264. In step 263the process checks whether the maximum DL power is greater than or lessthan the maximum permitted femtocell basestation DL power (a parameterset by the management system). If it is less than the maximum permittedpower, the maximum DL power remains at its re-set value. However, if themaximum DL power is greater than the maximum permitted power, themaximum DL power is changed to the maximum permitted power, and awarning sent to the management system. For example, a flag may be set toindicate that the maximum DL power is less than that required to run aparticular speech or data service.

In step 264 the process checks whether the maximum UL power is greaterthan or less than the maximum permitted femtocell basestation UL power(a parameter set by the management system). If it is less than themaximum permitted power, the maximum UL power remains at its re-setvalue. However, if the maximum UL power is greater than the maximumpermitted power, the maximum UL power is changed to the maximumpermitted power, and a warning sent to the management system. Forexample, a flag may be set to indicate that the maximum UL power is lessthan that required to run a particular speech or data service.

The whole process as described by FIGS. 6 and 7 repeats, adapting themaximum UL and DL powers until either an error event occurs, the powersconverge to an optimal value, or the host processor identifies thatthere has been a significant change in the local interference levels andthe carrier, scrambling code and initial UL and DL powers need to bere-evaluated.

Further, the value of minimum indoor loss is adapted as the processrepeats. For example, minimum indoor loss may be set at 60 dB initially.When the process is run, it may end up at step 262. IfPathloss_Adjustment is found to be 10 dB, minimum indoor loss is resetat 70 dB, and for the next repeat of the process, indoor loss will beginat 70 dB.

FIG. 8 is a flowchart of the preferred algorithm that may be used toadapt the UL and DL maximum transmit powers in the event that nointerference is detected from the macrolayer or the femtocellbasestation layer.

As described above, histograms are produced from the UE measurements.Specifically, these are the femtocell basestation to femtocellbasestation UE path losses, and the femtocell basestation UE CPICH Ec/lomeasurements. From these histograms, the following quantities can becalculated:

Avg_(—) Ec/lo=the average of the top 10% femtocell basestation UE CPICHEc/lo values;

Avg_FBL_Pathloss=the average of the top 10% FB to FB UE path losses;

Pathloss_adjustment=the absolute value of [½(Avg_(—)FBL_Pathloss−Maximum allowed FB Pathloss)]

Maximum allowed femtocell basestation pathloss is supplied by themanagement system, and based on an assumed maximum indoor path loss(typically around 90 dB).

Indoor loss is set at the value of minimum indoor loss, as describedwith reference to FIG. 7.

In step 270, Avg_Ec/lo is compared with the desired femtocellbasestation UE CPICH Ec/lo. If Avg_Ec/lo is larger, then the processmoves to step 274, which compares Avg_FBL_Pathloss with the maximumallowed femtocell basestation path loss. If Avg_FBL_Pathloss is smaller,the UL and DL maximum transmit powers are kept at the same level (step275).

If Avg_FBL_Pathloss is greater than the maximum allowed femtocellbasestation path loss, then the UL and DL maximum transmit powers areset as follows (step 276). Maximum DL power is set at UE_(Prx, min),plus the indoor loss, minus Pathloss_adjustment. Maximum UL power is setat FB_(Prx, min), plus the indoor loss, minus Pathloss_adjustment.Minimum indoor loss is reset at indoor loss minus Path loss_Adjustment

If it is determined, in step 270, that Avg_Ec/lo is smaller than thedesired femtocell basestation UE CPICH Ec/lo, the process moves to step272, where Avg_FBL_Pathloss is again compared with the maximum allowedfemtocell basestation path loss.

If Avg_FBL_Pathloss is smaller, the maximum DL power is set in step 277at UE_(Prx, min), plus the indoor loss, plus Pathloss_adjustment.Maximum UL power is set at FB_(Prx, min), plus the indoor loss, plusPathloss_adjustment. Minimum indoor loss is set at Indoor loss plusPathloss_Adjustment.

If Avg_ML_Pathloss is greater than Avg_FBL_Pathloss, then an error alertis sent to the management system (step 278).

Once the maximum DL and UL powers have been set in step 276 or 277, theprocess moves in parallel to steps 278 and 279. In step 279 the processchecks whether the maximum DL power is greater than or less than themaximum permitted femtocell basestation DL power (a parameter set by themanagement system). If it is less than the maximum permitted power, themaximum DL power remains at its re-set value. However, if the maximum DLpower is greater than the maximum permitted power, the maximum DL poweris changed to the maximum permitted power, and a warning sent to themanagement system. For example, a flag may be set to indicate that themaximum DL power is less than that required to run a particular speechor data service.

In step 279 the process checks whether the maximum UL power is greaterthan or less than the maximum permitted femtocell basestation UL power(a parameter set by the management system). If it is less than themaximum permitted power, the maximum UL power remains at its re-setvalue. However, if the maximum UL power is greater than the maximumpermitted power, the maximum UL power is changed to the maximumpermitted power, and a warning sent to the management system. Forexample, a flag may be set to indicate that the maximum UL power is lessthan that required to run a particular speech or data service.

The whole process as described by FIGS. 6 and 8 repeats, adapting themaximum UL and DL powers until either an error event occurs, the powersconverge to an optimal value or the host processor identifies that therehas been a significant change in the local interference levels and thecarrier, scrambling code and initial UL and DL powers need to bere-evaluated. Again, the value of minimum indoor loss is also adapted asthe process repeats.

The maximum DL transmit power will also be adapted based on reportedround trip time (RTT) measurements available from the femtocellbasestation and measured for each femtocell basestation UE. A histogramof the RTT measurements would be built up for all calls and the maximumDL transmit power adapted so that a predetermined number of RTT samples(typically 90%) are within the expected coverage area.

Furthermore, Random Access Channel (RACH) measurements can be used todetermine at what distance from the access point a mobile is trying toset up a call. If the call set up is outside of the expected coveragearea then the call can be rejected.

Error conditions such as multiple accesses from unregistered mobiles mayindicate that the DL coverage is too large or that the user haspositioned the femtocell basestation in a position that is causingunnecessary DL macrolayer interference (e.g. on a window overlooking thecity). In this situation the maximum DL transmit power may be reduceduntil this error event falls below a predetermined threshold.Alternatively, the problem could be reported to the management system,which may send a message to the user requesting him to relocate the unitin a position that would cause less interference. Thus the basestationcan use knowledge of access attempts by unregistered mobiles to adaptthe DL and UL maximum transmit powers.

As described above, there are several ways in which error conditions canbe detected, and may be reported to the management system. For example,there may be a requirement to use a particular power level, orinformation about a number of access attempts from mobiles that areoutside the intended coverage area. These may indicate that theconfiguration of the basestation would cause excessive interference, orotherwise be detrimental. In each of these situations, the problem maybe resolved by repositioning of the basestation, for example away from awindow or towards a position nearer the centre of the intended coveragearea. In response to an error condition, therefore, a message may besent from the management system to the user of the basestation,requesting that the basestation be repositioned. The message may bedisplayed on the basestation itself, or sent to a device that isconnected to the basestation. This repositioning can be carried outuntil the error condition is resolved, and therefore acts as apseudo-closed loop control.

There are thus described methods of operation of a basestation, andbasestations adapted for such uses, that allow the basestations toconfigure themselves for operation within the cellular network withoutexcessive interference with each other or with other basestations in thenetwork.

1-17. (canceled)
 18. A method of controlling a femtocell basestation ina cellular wireless communications network when interference with amacrolayer basestation is detected, the method comprising: obtaining aplurality of measurements of pathlosses between the macrolayerbasestation and one or more mobile devices having wireless connectionsto said femtocell basestation; determining a pathloss at a predeterminedpercentile of said plurality of measurements; and adapting a maximumvalue for a total transmit power of one or more mobile devices havingwireless connections to said femtocell_basestation based on saiddetermined pathloss at the predetermined percentile of said plurality ofmeasurements.
 19. A method as claimed in claim 18, wherein the step ofadapting the maximum value for the total transmit power of one or moremobile devices comprises: setting the maximum value for the totaltransmit power of the one or more mobile devices equal to the minimumsignal power required by said basestation to support a particularservice, plus said pathloss at a predetermined percentile of saidplurality of measurements.
 20. A method as claimed in claim 18, furthercomprising: determining a maximum value for the total transmit power ofthe one or more mobile devices; comparing the determined maximum valuewith a maximum permitted value for the total transmit power; and settingthe maximum value equal to the determined maximum value only if thisdoes not exceed the maximum permitted value for the total transmitpower.
 21. A method as claimed in claim 18, further comprising adaptingthe maximum value for the total transmit power of the one or more mobiledevices within the basestation, autonomously and dynamically.
 22. Amethod as claimed in claim 18, wherein, before the step of adapting themaximum value for the total transmit power of said one or more mobiledevices, there is the step of: determining whether or not a carrier thathas been selected for communicating with UEs is unused by neighbouringmacrolayer basestations or other basestations; wherein a carrier isunused if there are no detected macrolayer basestation or otherbasestation CPICH signals and the received signal strength indicator(RSSI) on the carrier is below a minimum interference threshold.
 23. Amethod as claimed in claim 22, further comprising the step of: if thecarrier is not unused by neighbouring macrolayer basestations or otherbasestations, determining whether the interference caused byneighbouring macrolayer basestations is greater than or less than theinterference caused by neighbouring other basestations.
 24. A method asclaimed in claim 23, further comprising, if the interference caused byneighbouring macrolayer basestations is greater than the interferencecaused by neighbouring other basestations, the step of: calculating thebasestation to neighbouring macrolayer basestation path losses.
 25. Amethod as claimed in claim 24, said step of adapting a maximum value fora total transmit power of one or more mobile devices comprising: if saidcarrier is unused by neighbouring macrolayer basestations or otherbasestations, setting the total transmit power of said one or moremobile devices at a first level; if said carrier is not unused byneighbouring macrolayer basestations or other basestations, and theinterference caused by neighbouring macrolayer basestations is greaterthan the interference caused by neighbouring other basestations, settingthe total transmit power of said one or more mobile devices at a secondlevel; if said carrier is not unused by neighbouring macrolayerbasestations or other basestations, the interference caused byneighbouring macrolayer basestations is less than the interferencecaused by neighbouring other basestations, setting the total transmitpower of said one or more mobile devices at a third level.
 26. A methodas claimed in claim 25, further comprising: determining whether saidfirst, second or third levels are greater than a maximum permitted powerthreshold; and if said first, second or third levels are greater than amaximum permitted power threshold, resetting the total transmit power ofthe basestation to said maximum permitted power threshold; and if saidfirst, second or third levels are not greater than a maximum permittedpower threshold, maintaining the total transmit power of the basestationat its set level.
 27. A basestation adapted to perform the methodaccording to any of claims 18-26.